Prokaryotes: The big picture


  • ‘Prokaryotes’ are not a monopheyltic group
    • Kingdoms Bacteria & Archaea; each with unique traits
    • most species diverse groups on Earth


  • Diversity of ways of making a living
    • sources of energy to make ATP
    • heterotrophs
    • autotrophs (photosynthesis)


  • Co-evolution with the planet and other organisms
    • oxygen poor to oxygen rich world
    • extremeophiles (temperature, pH, salt,etc.)
    • prokaryotes are most abundant organisms on Earth!

Prokaryotes do it all! (review Table 27.1)


  • Sources of carbon
    • autotrophs (make themselves)
      • chemically
      • light
    • heterotrophs (get from others)


  • Energy for ATP (no mitochondria)
    • sunlight
    • organic molecules
    • inorganic molecules


  • Lifestyles reflected in extensive genetic diversification


Picture: Iron-oxidizing bacteria are chemoautotrophic bacteria that derive energy by oxidizing ferrous iron

Prokaryotes need nitrogen and may need oxygen

  • Metabolism varies with respect to oxygen
    • use for cellular respiration
    • or poisoned by it!
    • some can extract chemical energy from nitrite or sulfate


  • Nitrogen is essential for production of amino acids
    • prokaryotes less limited in obtaining nitrogen


  • Some bacteria convert atmospheric nitrogen (N2) into usable forms
    • termed Nitrogen fixation


  • Picture: Bacteria work together
    • photosynthesis and N fixation

Metabolic cooperation leads to Biofilms


Biofilms are living communities that allows microorganisms (such as single-celled bacteria) to behave as a group


  • Fossil evidence of biofilms dates to about 3.25 billion years ago


  • More than 75% of human infections are thought to be related to the presence of microorganisms in the form of biofilms
    • on the surface of tissues or medical devices
    • dental plaque!

Rapid reproduction leads to high genetic diversity

  • Rapid reproduction and large populations leads to many mutations
    • not through sexual reproduction
    • 2 x 10^10 new E.coli cells in human intestine each day
    • possible for millions of mutations each day
    • infant microbiome diversifies rapidly based on environment..

Reproduction in prokaryotes: Binary fision


  • Asexual: daughter cells identical to parent
    • rapid reproduction
    • not sustainable!
    • not great for genetic diversity


  • Mutations are rare but fast reproduction


  • Gene transfer increases diversity:
    • transformation =
    • transduction =
    • conjugation =

Genetic Recombination: Transformation

Genetic Recombination: Conjugation (mechanism unresolved)

Prokaryotes are incredible diverse


  • Acutally a big assumption!
    • only 16,000 described


  • Genomes are super diverse because of horizontal gene transfer


  • Bacteria: prokaryotic species most commonly known
    • pathogens to yoghurt


  • Archaea: share traits with bacteria and eukaryotes
    • earliest ancestors in extreme environments

Prokaryotes matter: Oxygen Revolution

Prokaryotes matter: Cynaobacteria


  • Cyanobacteria: first evidence ~2.7 bya
    • blue-green algae
    • aquatic and photosynthetic
    • use chlorophyll


  • Photosynthesis evolved independently in distant groups
    • mono, para or polyphyletic?
    • cyanobacteria are a monophyletic group


  • Eukaryotes acquired photosynthesis by engulfing cyanobacteria!

Prokaryotes matter: Great Oxygenation

Prokaryotes matter: Chemical Recycling

Prokaryotes matter: Species Interactions

Prokaryotes matters: Humans